Japanese Prime Minister Junichiro Koizumi has lodged a formal protest with Russian President Vladimir Putin over a fishing rights dispute. Mr. Koizumi says that, if the issue goes unresolved, it could gravely affect bilateral ties between the two nations.

For the second time in a month, Japan is protesting Moscow's decision to grant permits to third countries to fish in waters off four disputed islands, near the northern Japanese island, Hokkaido.

Both Russia and Japan lay claim to the islands and their surrounding waters. The Kuril Islands, known as the Northern Territories in Japan, were seized by the former Soviet Union at the end of World War II.

With Moscow's permission, South Korean boats began fishing in the area, earlier this month. Russia has also granted fishing rights to North Korea and a Ukrainian fishing firm. The Ukrainian company subsequently sold the rights to a Taiwanese fishing group.

Monday, Japanese Foreign Minister Makiko Tanaka summoned the Russian ambassador to Tokyo and gave him the letter of protest from Prime Minister Koizumi for Russian President Vladimir Putin. In the letter, the Japanese leader urged Mr. Putin to avoid a worsening dispute. Mr. Koizumi says Tokyo cannot accept the current situation, which he describes as deplorable. He warns that it could hinder the two nations' efforts to sign a peace treaty formally ending the hostilities of World War II.

Japanese Foreign Minister Makiko Tanaka spoke with reporters Monday and underscored the prime minister's concern. She said Russia gave fishing permission not only to South Korea but to other countries, as well. She adds that Japan's propositions on resolving the issue have, so far, been ignored.

South Korean fishing activities in the disputed islands further strained relations between Tokyo and Seoul - already damaged by a controversial Japanese history textbook and Mr. Koizumi's war shrine visit last week.

Japan says, by fishing in the disputed waters, South Korea is violating Japanese law as well as a fisheries pact between the two countries. But Seoul says its fishing deal with Russia has no political significance and is standard international practice.